This one is pretty hard to test. It comes down to the size of your pipe vs the amount of traffic being sent by the attackers. To mitigate the attack you will need to work with your upstream providers(s) to stop the traffic before it even gets to you. I know this isn't much of an answer but I don't know what else to tell you.

chrisj wrote:It's more than just the size of the pipe. Filling the pipe is the fastest way, but if you have something without enough power behind the pipe, then they can DDOS by taking that off line too.

Good point, if your server does some action that uses a lot of resources (like maybe search) then it would be easy to use all of the resources of the server.

My assumption is that he was taking a utilized the pipe since he referenced trying to stop it based on geography. Bad assumpton